This invention relates to novel compounds expressed by the following general formuula: ##STR4## where R is ##STR5## a pale yellowish oily substance having an optical rotation of [.alpha.].sub.D.sup.24 -121.degree. (C=0.75, ethanol), a molecular weight of 420 estimated from peak value in mass spectrum measurement (theoretical value: 420), a molecular formula of C.sub.22 H.sub.28 O.sub.8, an end absorption at 210 mm (.epsilon.:14800) in ultraviolet absorption spectrum, peaks in infrared absorption spectrum by liquid film method at the frequencies (cm.sup.-1) of 3400, 2920, 2845, 1760, 1740, 1705, 1658, 1440, 1370, 1325, 1220-1280, 1180, 1133, 1107, 1070, 1020, 970, 881, 840, 819, 788, 758, 710, 662, 630, 607 and 582, assignments of respective protons in NMR spectrum (.delta., CDCl.sub.3) at C.sub.6 --H=5.96 (1H, dd, J=11,2), C.sub.4 --CH.sub.3 =1.80 (3H, d, J=1), C.sub.10 --CH.sub.3 =1.84 (3H, s), C.sub.3' --H=6.90 (1H, t, J=5.5), C.sub.4' -- H=4.37 (2H, d, J=5.5), C.sub.5' --H=4.31 (2H, s), exo CH.sub.2 =5.79,6.33 (1H, d, J=2), COCH.sub.3 =2.12 (3H, s); ##STR6## or [III] hydrogen; and a process for the preparation of these substances.
Recently, analytical research into the components of the various plants belonging to the genus Eupatorium has been pursued by Kupchan et al (J. Org. Chem. 38, 1260, 2189 (1973)), and various compounds having a significant antitumorigenic effect have been isolated. Among these compounds, those having the germacrane skeleton include the following: ##STR7## and it is known that these compounds show an inhibitory effect against growth of the cancer cells in the in vitro tests on the experimental cancer cells.
As a result of many experimental separation and refining of the extracts from Eupatorium sachalinense, a plant belonging to the genus Eupatorium, the present inventors have succeeded in isolating three novel substances (I, II and III) of the germacrane system, and it was clarified from various spectral analytical data and chemical reactions that these substances have the following chemical structures:
______________________________________ ##STR8## ##STR9## (Hiyodorilacton-A) ##STR10## (Hiyodorilacton-B) III : R = H (Hiyodorilacton-C) ______________________________________
The compound I obtained from the plants belonging to Eupatorium is a stereoisomer of eucannabinolide which is described by B. Drozdz et al (Collection Czechoslov Chem. Commun. 37 1546 1972)) and by M. Holub et al (ibid 42 1053 (1977)) and of eupaformosanin which was described by Kuo-Hsing et al (Phytochemistry 16 1068 (1977)), eucannabinolide and eupaformosanin having the structures as indicated below. ##STR11##
Compound I is same as the compounds IV and V in plane structure but has the acetoxyl group on the mother ring in beta-position in contrast the alpha location of the counterpart in compound V.
Upon comparing the physical properties of compound I with the corresponding data for compound IV given by B. Drozdz et al, the two compounds are found to have same appearance, optical rotation and molecular weight and exhibit peaks at similar frequencies in their infrared absorption spectra. However, in NMR spectrum, the hydrogen signal of the methylene group at C--4' of the side chain appears at .delta.4.37 (d, J=5.5) with compound I, in contrast to .delta.4.00 (d, J=6.0) of compound IV.
Compounds I and IV are identical with respect to the structure of the mother ring but they are considered to be stereoisomers with respect to the side chain.
Although it is not known whether the compounds IV and V have anticarcinogenic activity, the compounds I to III according to the present invention have been ascertained to have not only high inhibitory effect against growth of experimental cancer cells (HeLa) when used even in a low concentration, but also considerable life prolonging effect in the in vitro experiments on mice inoculated with Ehrlich ascites cancer cells, suggesting availability of these substances as a medicine for malignant tumors in humans.
The compounds I to III are contained throughout the body of the plant including root, stems and leaves, but since they exist in greater concentration in the leaves, it is advantageous to use the leaves as their extraction source.